(na3c6h5o7) solution affect the conducivity (ms/m) of the ... · the mechanism of this reaction...

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Research Question: How does the Oxidation duration (0,2,4,6,8,10 hours) of Sodium Citrate

(Na3C6H5O7) solution affect the conducivity (mS/m) of the solution; by measuring the changes in

the current pasing through the solution using a constant voltage of 9V?

Introduction:

The mineral ions in Pocari Sweat are mostly Sodium Citrate ions according to the official website

(Otsuka, 2017).

Investigation:

Main equation for the reaction:

Symbol Equation: C3H5O (COO)33−

(aq)+ H2O(l) ⇌ HC3H5O(COO)32-

(aq)+ OH-(aq)(Minotti & Aust, 1987)

Word Equation: Citrate ion3-

+ Water ⇌ Oxalosuccinate2-

+Hydroxide Ions

The equation (above) is the reaction showing the oxidation (losing of electrons) of citrate ions; this

reaction is induced by electrolysis whereby one electron is lost by C3H5O (COO)33−

ions this process.

This reaction occurs when the electrolyte is dissolved into water. The electrolyte is the same

concentration as (Wolf, 1966) allowing for a comparison of experimental conductivity data with

literature values. This reaction is an oxidative hydrolysis reaction (Minotti & Aust, 1987). The

concentration of citrate ions affects the conductivity of the solution.

The mechanism of this reaction involves the Citrate ions (already dissolved in the solution) are further

oxidised to form Oxalosuccinate ions when dissolved into water (Minotti & Aust, 1987). In

electrolysis, hydroxide ions are attracted to the anode and hydrogen ions to the cathode which in turn

allows for the completion of a circuit and the reduction and oxidation of the two respective ions.

Joseph Ong

Figure 1- Mechanism of electrolysis

Na3C6H5O7 (Sodium

citrate solution)

Na+ and C3H5O (COO)33- are

in the solution.

Cathode: OH-(aq)

1

2O2(g)+

1

2H2O(l)+e

- Anode: H+

(aq)+e-

1

2H2(g)

(Hewitt, 2004)

After a game of tennis, my favourite drink to consume is Pocari Sweat. Given my personal

experiences with this drink, I conducted some research and found that in Japan this drink is given to

students before exams - by Japanese parents. One thing I found strange was that some parents

would oxidise the solution for a certain duration before giving it to a student on the examination

day. One parents claimed that the mineral content (which I found to mostly be Na3C6H5O7) would

“stimulate neurological activity by providing the brain with more minerals” – if the drink is left out

over time. I highly doubted this theory and so I wondered how exactly the conductivity of this ionic

drink is actually affected with the time it is left out as this should also be dependent on the ionic

concentration that could change with oxidation duration.

*The conductivity is affected by the

concentration of mobile citrate ions because

the lower the ionic concentration, the lower

the conductivity of the electrolyte.

ALL RIGHTS BELONG TO OWNERTAKEN FROM WWW.INTERNALASSESSMENTS.WORDPRESS.COM

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Electrolysis is a process that drives redox reactions with dissolved ions. These ions transfer current

between electrodes and depending on the concentration of mobile ions, the current recorded varies.

However, with time oxidising reactions (reference main equation, above) reduce the concentration of

citrate ions in solution. This most likely is done with oxygen being dissolved from the air to oxidise

the citrate anions. The concentration shall be 9.88×10-2

mol dm-3

(±0.00098) the same concentration

as (Wolf, 1966) as it will allow the experimental values at 0h to be compared with a literature value to

determine the uncertainty and the reliability of the experimental values.

*Conductivity is a solution’s ability to pass an electric current. (Hewitt, 2004).

HL Background Information of conductivity:

𝑲 =𝑳

𝑨𝑹 be Equation 1 (College, n.d.) For Equation 1: K is conductivity (Sm

-1), 𝑳 is the length of

wire (m), A is cross-sectional area (m2), and R is overall resistance (Ω) of the solution (including the

electrolyte).

It is axinomatic that the K-value (conductivity) of a solution will decrease with the resistance of the

solution, as K is inversely proportionate to R. In accordance with Ohm’s law𝑅 =𝑉

𝐼. Therefore,

changes in the electrolyte resistance will result in changes to the concentration of the electrolyte.

Figure 2- Graph showing conductivity against resistance, demonstrating the inversely proportional relationship between

resistance and conductivity (S/m) (Hewitt, 2004)

Calculations used to produce the sodium citrate electrolyte:

Calculations of concentration= 5.1𝑔 (±0.05𝑔)

258.06× 0.5(±0.0005c𝑚3) = 9.88 × 10−2 mol d𝑚3 =

𝑚𝑎𝑠𝑠

𝑀𝑟× 𝑣𝑜𝑙𝑢𝑚𝑒

Uncertainty calculation = (0.05

5.1× 100%) + (

0.0005

5× 100%) = 0.0005 + 0.98 ≈ ±0.99%

Absolute uncertainty = 0.99

100× 9.88 × 10−2 = ±0.00098 mol dm

-3

Introducing the calculations required to calculate conductivity:

Calculation proceedures:

1. Calculating resistance (Ω) at 9V and measured current (A) values at each oxidation duration.

2. Calculate conductance by inversing resistance value (done by dividing one by resistance

value).

Conductivity


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3. Calculating the cross sectional area (Acm2) of the electrolyte by multiplying the height (cm)

and length of the beaker (cm).

4. Multiply condutance (Ω-1

) by length of beaker (cm) and divide value by cross sectional area

(cm2) to get conducativity (Siemens)

5. Multiply conductivity by 1000 to get conductivity in millisiemens which is the same as (Wolf,

1966).

Hypothesis

The conductivity will decrease as the greater the oxidation duration of the solution. This is

because the oxidation reaction of citrate ions is spontaneous (Randall & Templeton, 1991). Therefore,

with time (h) the solution will oxidise and the number of ions in the solution will decrease. When a

more dilute solution (with more oxidised ions) is used as the electrolyte contains less mobile ions the

charge carried would likely decrease - changing the overall resistance of the circuit. As the lower the

ionic concentration of mobile citrate ions, the lower the conductivity of the solution. When

oxidisation occurs, the concentration of mobile citrate ion is reduced leading to the conductivity of

sodium citrate to be reduce as oxidation duration increases.

During this investigation the only thing studied was the conductivity of the solution. However, it was

assumed that this could only be affected by concentration of the electrolyte. Therefore, several

variables were controlled in order to measure how the concentration, and subsequently the

conductivity were affected by the duration of oxidation.

Methodology

There are two parts of the methodology used to determine the conductivity based on oxidation

duration. 1) Producing and oxidising a sodium citrate electrolyte 2) Electrolysing sidum citrate

to measure resistance by measuring current and then calculating conductivity. These two

methods were modified established methods adapted from the Journal of International Environmental

Sciences (Ahmet Alıcılar, 2008) and the Biomedical Researchers from Yale University (Lobo, 2017).

Modifications made to the oxidation methodology (Ahmet Alıcılar, 2008)

a. The chemical used was sodium citrate instead of Iron Suplphide Hexahydride, as that is the

primary chemical under investigation.

b. The lab’s absence of a T-piece, to pump air into the centre of a solution meant that

adjustments had to be made to the original method which required a T-piece; prolonging

oxidation duration (independent variable) instead of increasing the air flow into the centre of

the Sodium Citrate solution. However, this may cause evaporation of water during this

duration as well.

Modifications made to the electrolysis methodology (Lobo, 2017)

I. This method did not factor in distance apart of electrodes. Therefore, I chose to control this

variable (reference control variable section).

II. Instead of a conductivity sensor (prescribed by the method) I used a ammeter as our

laboratory did not have a conductivity sensor.


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List of apparatus

1. Memmert Water Bath (±0.1°C) set to 25.0°C

2. 5.1g (±0.05g) of Sodium Citrate powder for each experiment (per 5 experimental repeats)

(this is to produce a concentration similar to that used by (Wolf, 1966) allowing for a

comparison of these quantitative results and a literature value.

3. Mass Balance (±0.01g)

4. 500cm3 (±0.5cm

3) of distilled water and 500cm

3 beaker

5. Five 100 cm3 beaker

6. 500cm3 (±0.05cm

3) volumetric flask

7. 100cm3 (±0.05cm

3) volumetric flask

8. 2 three centimeter graphite electrodes

9. Ammeter (±0.005A)

10. Battery pack (9V)

11. 4 copper wires with alligator clips.

12. Stopwatch (±0.01s)

13. Ruler (±0.1cm)

14. Spatula

15. Tongs

16. Thermometer (±0.1°C)

Methodology used in order to produce and oxidise the Sodium citrate electrolyte

1. Using a spatula add 10.0g (±0.01g) of Sodium Citrate powder to 500cm3 (±0.05cm

3) of

distilled water (measured using a volumetric flask before adding to a beaker).

2. Using a glass rod, stir the powder and ensure that it is fully dissolved into the solution (with

no crystals left undissolved).

3. Set the Memmert water bath to 25.0°C (±0.1°C) by adjusting the knob.

4. Decant 100cm3 (±0.05cm

3) of the Sodium citrate solution into a 100cm

3 volumetric flask and

then into a 100cm3

beaker and place the beaker into the Memmert water bath for desired

oxidation duration.

5. Remove the beaker carefully using tongs to prevent mechanical injuries.

6. Repeat steps 1-5 five times for each oxidation duration (0,2,4,6,8,10 hours)

Figure 3- Electrolysis experimental set-up

Battery pack (9V)

Sodium citrate

electrolyte

Graphite electrodes

(5cm apart measured

using ruler)

Ammeter (A)

Copper wires (with alligator clips

connecting wires from batter to

graphite electrodes)

Ruler (used to calculate the

cross section area and height

of beaker and distance apart

of electrodes


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Methodology used in order to find out the electrical current passing through circuit:

1. Add two electrolytes (3cm length) connected to a battery pack of 9V, using copper wires with

alligator clips, to the oxidised solution of sodium citrate. Ensure that electrodes are exactly

5cm (±0.1cm) apart as measured with a ruler.

2. Connect two copper wires to an ammeter in a parallel circuit.

3. Switch on the battery pack (reference step 1)

4. Record the current recording as displayed on the ammeter (±0.01A) after electrolysing

sodium citrate for 30 seconds – this time duration was determined using a preliminary trial

whereby the readings were found to remain constant after around 30s.

5. Repeat steps 1-5 five times for each oxidation duration (0, 2, 4, 6, 8, 10 hours). This will

provide a total of 30 raw data sets which shall be processed.

6. Using a ruler, also measure the height of the beaker and the overall area of the beaker to find

out the A and L values (reference Equation 1, page 1 for full equation).

Monitoring lab conditions

a) Thermometer was placed in the water around the oxidising electrolyte to ensure constant

temperature.

b) Air-conditioning was maintained at 25.0°C for the entire experiment.

Dimensions of a beaker

Figure 3- The proportions of a beaker

Safety Precautions:

Sodium Citrate can cause mild irritation to the skin and eyes. Therefore, gloves, lab coats and goggles

were worn throughout the experiment. Additionally, Sodium Citrate was disposed of in a sealed

container and sent off to a processing company to handle. Environmental hazards could be the

animals such as birds consume citrate or sodium ions which can lead to renal failure and subsequently

disrupt food chains. While handling using electricity, extra care was taken to not spill any of the

Sodium Citrate solution (or any other liquids) onto the battery pack to prevent an electrical shock.

While using water baths, tongs were used to place beakers of Sodium Citrate into the solution as well

as to remove the beakers from the water bath to prevent mechanical injury due to heat.

6cm. This is the Height of

the electrolyte solution.

5cm. This is the

Diameter of the

electrolyte

𝐶𝑟𝑜𝑠𝑠 𝑆𝑒𝑐𝑡𝑖𝑜𝑛𝑎𝑙 𝐴𝑟𝑒𝑎

= 𝐻𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑒𝑙𝑒𝑐𝑡𝑟𝑜𝑙𝑦𝑡𝑒

× 𝐷𝑖𝑎𝑚𝑒𝑡𝑒𝑟 𝑜𝑓 𝐸𝑙𝑒𝑐𝑡𝑟𝑜𝑙𝑦𝑡𝑒

*Note that the cross sectional area, or A

(reference Equation 1 on page 1). Can

be calculated using the formula

*photo not to scale


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Variables

Table 1- Independent, Dependent and Controlled variables for the experiment

Type Variable Purpose How this was

achieved

Independent Oxidation duration (0, 2, 4, 6,

8,10 hours) of Sodium citrate.

With 5 repeats for each

duration.

This was to provide sufficient

data sets in which to obtain

results from

Using a stopwatch the

number of hours of

oxidation was timed.

Dependent Conductivity of the sodium

citrate solution

This dependent variable was

measured to investigate effect of

oxidation duration on the

conductivity of the solution.

Measured by the

reading the ammeter

reading after 30s as a

raw data. This is then

processed to calculate

solution conductivity.

Controlled

Variables

Initial concentration of sodium

citrate solution was kept at

9.88 × 10−2mol dm-3

That way oxidation process can

be measured with changes in

recorded current. Done by using

the same masses of sodium

citrate and volume of distilled

water.

This was done by

using dissolving the

same mass of sodium

citrate (5.1g) into the

same water volume

(500cm3). Air-

conditioner was kept at

25.0°C for the entire

day. Distance (cm) apart of

electrolytes

This ensures that the current is

not affected by the distance apart

of the electrodes.

This was measured

using a ruler and along

the diameter of the

beaker.

Temperature (°C) at which

oxidation occurs

This ensures that a constant rate

of oxidation occurs over the

different time durations and that

temperature did not change the

electrolysis rates.

Placing the sodium

citrate electrolyte into

the Memmert water

bath set to 25.0°C for

specified oxidation

duration.

Electrode composition This ensures that all

experimental repeats have the

same electrodes and have no

additional electron inference that

many affect current measured.

Graphite electrodes

were used for all

experimentation. This

is because graphite has

inert electrons.

Time for electrolysis This was required because as

electrolysis occurs the number of

ions is reduced. To provide

sufficient time for ammeter to

adjust, without depleting too

many ions,

Using a stopwatch the

number of seconds the

electrolyte was

electrolysed was timed.

Same apparatus used To ensure no factors such as the

conductivity affect the

conductivity of the device.

The same length of

copper wires, battery

pack and ammeters

were used for all sets

of experiments.

Light intensity Some electrons can be excited

with the addition of photons and

so electrolysis can occur faster if

light intensity increases.

Drawing the curtains

throughout the

duration of the

experiment.


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Raw Data

Calculating Average current for 0h

0.42 + 0.42 + 0.42 + 0.42 + 0.42

5= 0.42𝐴(±0.005𝐴)

Qualitative analysis

1. Occasionally the milliseconds part of the stopwatch were different for each timing

2. Electrolyte volume was reduced slightly after being left to oxidised (observed by reading beaker

measurements).

3. Colourless gas was observed coming off both electrodes due to electrolysis.

4. Reading on the ammeter stayed constant at around 30s before plummeting after 180s.

5. The rate of effervescence decreased as oxidation duration increased.

6. No changes in electrolyte colour were observed.

7. Slight decrease in volume of the electrolyte in the beaker after the specified oxidation duration.

This volume decreased more the greater the time duration of the oxidation. Due to increased

evaporation.

8. Slight bit of rust of the crocodile clips.

Sample Calculations of conductivity for 0h oxidation durations

Current (A) (±0.005A) measured when

electrolysing sodium citrate

Time (h)

(±0.01seconds)

Repeat

1

Repeat

2

Repeat

3

Repeat

4

Repeat

5

0 0.42 0.42 0.42 0.42 0.42

2 0.40 0.40 0.40 0.40 0.41

4 0.36 0.36 0.36 0.36 0.36

6 0.32 0.32 0.33 0.33 0.32

8 0.33 0.33 0.33 0.33 0.33

10 0.31 0.32 0.31 0.32 0.32

Dimensions of the

electrolyte

Measurements of the

Length and Height

values

Height of electrolyte

solution (cm). This is

shall be referred to as

H in table 4

6.0 (±0.1cm)

Diameter of

electrolyte solution

(cm).

This is shall be

referred to as L in

table 4

5.0 (±0.1cm)

Table 2- Raw data of the current (A) passing through solution obtained from

the prescribed methodology using an ammeter

Current (A)(±𝟎. 𝟎𝟎𝟓𝐀)

Time (h)

(±0.003h)

Repeat

1

Repeat

2

Repeat

3

Repeat

4

Repeat

5

0 0.42 0.42 0.42 0.42 0.42

2 0.40 0.40 0.40 0.40 0.41

4 0.36 0.36 0.36 0.36 0.36

6 0.32 0.32 0.33 0.33 0.32

8 0.33 0.33 0.33 0.33 0.33

10 0.31 0.32 0.31 0.32 0.32

the prescribed methodology

using an ammeter

Table 3- Raw data of the dimensions of the beaker

shown in figure 3 using a ruler.

Table 3- Raw data of the dimensions of the beaker

shown in figure 3 using a ruler.

Table 4- Sample calculations of all variables at 0h oxidation duration for sodium citrate electrolyte

Final

answer

obtained is

also 2SF

Random

error is also

2SF

Note* Raw

data SF is 2

because the

ruler used to

measure

dimensions

is only

accurate to

2SF)

Raw data SF

is equal

Final data SF

Note* SF means

Significant figures

1.19% + (0.1 × 2

5+

0.1

5)

× 100% = 7.19%


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Processed data table

Table 4- Processed data table showing conductance, cross sectional area, and conductivity of sodium citrate electrolyte

Time (h) (±0.003h) Conductance (S-1

)

Cross-sectional area of

the beaker (cm2)

(A)(±0.2cm2)

Conductivity (mS)

(millisiemens) (2SF)

0 0.0462 25.0 9.2

2 0.0444 25.0 8.9

4 0.0400 25.0 8.0

6 0.0367 25.0 7.3

8 0.0367 25.0 7.3

10 0.0353 25.0 7.1

Literature value of the conductivity after 0 hours of oxidation 7.4mS (Wolf, 1966)

(Reference sample calculations for 0h values, all other conductivity values for different oxidation durations were obtained

using Microsoft excel)

Graph showing the effects of oxidation duration and conductivity

To explicitly see the effects oxidation duration has on conductivity, the average conductivity

(dependent variable) is plotted against the oxidation duration (independent variable) below.

Interpreting the graph:

A negative correlation can be observed between the oxidation duration of sodium citrate (h) and the

conductivity of sodium citrate (mS) in Graph 1. The maximum conductivity data point recorded was

at 0h whereby conductivity is 9.2mS. The minimum conductivity data point recorded was at 10h

Graph 1- Conductivity of sodium citrate against oxidation duration

*Error bars

represent the

absolute

uncertainties of

each conductivity

value (mS)

y = -0.2317x + 9.1365 R² = 0.9179

6

6.5

7

7.5

8

8.5

9

9.5

10

0 1 2 3 4 5 6 7 8 9 10

Co

nd

uct

ivit

y (m

S)

Oxidation duration (h)

The effect of oxidation duration (h) on conductivity (mS) of sodium citrate

Negative correlation

Error Bars

represent

High R2 value


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whereby conductivity was 7.1mS. Overall the points are well represented with a high R2 value of

0.9179 which means that the line of best fit is very representative of the points it passes through and

that the trend is reliable (the closer the R2 value is to 1, the more reliable it is). Overall, the data

mostly agrees with the hypothesis that “the greater the oxidation duration, the lower the sodium citrate

conductivity”. An anomalous result is at 8 hours which had a 7.3mS conductivity value (the same

value as the 6h reading which was unexpectedly low). This makes it anomalous because this should

not have been the case given that after 8h of oxidation the conductivity of sodium citrate should be

less than after 6h of oxidation. This ‘anomaly’ can be interested as either forecasting a plateau or

could be attributed to random errors given the uncertainty of the experiment.

Table of uncertainty calculations (sample calculation available on page 7)

Table 3- Table of absolute conductivity uncertainties

Time (h)

(±0.003h)

Conductivity (mS) (mS stands for millisiemens) Percentage

uncertainty

(%)

Absolute

uncertainty

0 9.2 ±7.2 ±0.7

2 8.9 ±7.3 ±0.6

4 8.0 ±7.4 ±0.6

6 7.3 ±7.5 ±0.6

8 7.3 ±7.5 ±0.6

10 7.1 ±7.6 ±0.5

Percentage error calculations

To investigate the reliability of this experiment the value 9.2mS (the experimental conductivity value

with 0h of prior oxidation), will be compared with the (Wolf, 1966) value of 7.4mS in order to

determine the overall percentage error for the same Sodium citrate electrolyte concentrations. This

calculation is necessary in order to investigate how unreliable the experimental data is relative to more

accurate secondary sources and the literature value for a starting point. This would allow for the

investigation of the reliability of the obtained experimental values.

𝐸𝑥𝑝𝑒𝑟𝑖𝑚𝑒𝑛𝑡𝑎𝑙 𝑝𝑒𝑟𝑐𝑒𝑛𝑡𝑎𝑔𝑒 𝑒𝑟𝑟𝑜𝑟 =9.2 − 7.4

7.4× 100% = 24.3%

Conclusion

In conclusion, the results of the experiment agree with the hypothesis that “The conductivity will

decrease as the greater the oxidation duration of the solution”. The trend shows that the longer

the oxidation duration, the higher the sodium citrate electrolyte’s conductivity. According to

graph 1, the conductivity of the solution steadily decreases as the duration of oxidation increases

(negative correlation). The graph demonstrated a significant overall decrease in conductivity of 2.1mS

over the course of 10 hours of oxidation.

However, while the data is well represented by the “line of best fit” – as determined with the data’s

high R2 value of 0.92 – anomalies are present. Outliers can be observed, in conductivity the trends

between the 6 and 8 hour oxidation durations, whereby conductivity decreased at a decreasing rate.

Also, the relatively small change in conductivity that occurred between 8 to 10 hours (compared to the

large change in conductivity between 4 to 6 hours) (reference graph 1) results imply that oxidation


10

rates slow with time as fewer citrate ions are left for oxidation as time passes. This is because mobile

ions are necessary to carry electric charge (Brown & Ford, 2014). As a result, the rate of change in

conductivity is reduced with every passing hour. It would be an interesting area for further

investigation to prolong the oxidation duration to see if the conductivity of sodium citrate eventually

plateaus with more than 6 oxidation durations.

While the linear graph is reasonably representative (with the high R2 value), if the results later plateau

a curve of exponential decay would represent this trend better, however, within the scope of this

experiment a linear graph suffices.

Calculating Systematic Error to determine how much error was attributed to methodological

limitations.

𝑆𝑦𝑠𝑡𝑒𝑚𝑎𝑡𝑖𝑐 𝑒𝑟𝑟𝑜𝑟 = 𝐸𝑥𝑝𝑒𝑟𝑖𝑚𝑒𝑛𝑡𝑎𝑙 𝑒𝑟𝑟𝑜𝑟 − 𝑅𝑎𝑛𝑑𝑜𝑚 𝑒𝑟𝑟𝑜𝑟 = 24.3% − 7.2% = 17.1%

One could have relatively high confidence in experimental results, as the mean random error is 7.2%

is still relatively low and an evident trend is present. However, there still is quite a large percentage

error of 24.3% – from the literature value of Sodium citrate conductivity obtained by (Wolf, 1966)

(reference 15.1 calculations) which is likely attributed to the 17.1% systematic errors based on the

literature value at 0h of oxidation (which are highlighted and evaluated in the evaluation section).

7.4mS was the expected conductivity of the sodium citrate solution with 0 hours of oxidation, but

mine was 9.2mS. Despite the systematic errors causing most of the percentage error, the percentage

error is 24.3% relative to (Wolf, 1966) for the initial conductivity value. The hypothesis is true.

Evaluation:

Table 5- Table of experimental strengths

Strength Justification

Relatively low random error. This is only 7.4% meaning that apparatus used was

relatively accurate.

High R2 value. This means that the processed data is highly well

represented by the 0.91 R2 value which means that the

line of best fit is highly representative of the points it

passes through (as the R2 value is relatively close to 1.0)

Graphite electrons were used. This ensured that electrodes had inert electrons and that

no additional electrons were delocalized into the solution.

Temperature and pressure were controlled variables by

using equipment such as water baths.

This ensured that nothing else that could have affected

the rate of electrolysis by changing ionic concentration of

sodium citrate was present. This was done by leaving

experiment in a 25°C Memmert water bath. Oxidation of

citrate ions occurred in the better-controlled water bath

environment.

Low standard deviations and variance amongst data sets. Standard deviation is a representation of variance and

since this is low means that data used for each repeat is

over a very small range. As a result, few outlying

anomalies that could undermine the methodology or the

hypothesis are present.

Same electrodes used This ensured that no external electrons from the

electrodes interfere with the experiment as graphite

electrons are inert

Usage of volumetric flasks and highly accurate mass

balance were used

This ensures that the concentration of the sodium citrate

electrolyte was not altered as the apparatus use to obtain

it had low uncertainty.


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Experimental limitations

Table 6- Table of experimental limitations

Limitation Significance Improvement

Electrolysis as a method used to

measure conductivity may have

induced oxidation of citrate ions

(systematic error).

If oxidation of citrate ions

occurred. Less citrate ions would

be able to carry charge – reducing

the recorded conductivity.

Shorten the time of electrolysis to

avoid the oxidation of citrate ions

(electrolysis speeds this up).

Other reactions besides oxidation may

have caused the trend to decrease

(systematic error).

This may have overestimated the

effect oxidation duration has on

the conductivity of sodium citrate.

Use the same duration but include

the T-piece in the initial

experiment (Ahmet Alıcılar,

2008). This would ensure that

during that period of time more

oxygen was pumped at a constant

rate into the solution (through the

T-piece). This would mean that

most decreases in concentration

would be due to oxidisation of

citrate anions.

The Sodium citrate salt was exposed

to the air (systematic error).

This meant oxidation (due to water

particles in the air) may have

occurred prior to experimenting

Contain the Sodium citrate salt in a

vacuum. This will ensure minimal

exposure to elements like water

vapour.

An insufficient range of independent

variables were obtained (systematic

error).

Oxidation is a relatively gradual

process and only having a small

scope of 10 hours means the

conclusion is only valid for a small

range.

Increase the range of independent

variables for up to 72 hours to

fully investigate the effects of

oxidation duration on Sodium

citrate concentration.

Measuring equipment was not precise

enough (random error).

This increased random error in the

experiment. The main one is the

ruler used to measure proportions

of beaker

Using a Vernier Callipers

(±0.01cm uncertainty) instead

would provide a more certain

reading than the ruler (±0.1cm)

Insufficient number of repeats per

oxidation duration (random error).

Can lead to parallax error and

human reaction time delays (as

noted in qualitative analysis,

sometimes a few milliseconds of

oxidation or electrolysis occurred).

This could lead to incorrect

measurements used or incorrect

concentration obtained.

Ensure to do more experimental

repeats.

Evaporation occurred (reference the

change in volume with time in in

qualitative analysis) (systematic

error).

This would have increased the

concentration of ions – thereby

increasing the conductivity of the

solution.

Place a lid on the oxidising beaker

(while placed in water bath) to

minimise the effects of

evaporation.

Rust on the crocodile clips

(systematic error).

The lessening of pure metal mass

within the crocodile clips inhibits

current which increases resistance

thereby decreasing the measured

conductivity of solution.

Ensure to use a rust-free crocodile

clip or use sandpaper to scrap off

the Iron (III) Oxide on the

crocodile clips.


12

Further investigation

This investigation could include a greater range of independent variables to investigate how oxidation

duration affects the conductivity. In addition to this, other factors that affect the conductivity of the

sodium citrate electrolyte could be investigated. This includes the addition of an enzyme called citrate

synthase which provides an alternative pathway for citrate ions to oxidise. How does the

concentration of citrate synthase affect the subsequent conductivity of a sodium citrate

electrolyte? This alternative investigation would be useful as it would allow conclusions to be drawn

as to how the presence or absence of this enzyme in the blood affects the way electrical impulses

travel from the brain. This would allow for a better understanding of the neurological activities of the

brain (as this model could be applied to the brain).

Bibliography

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Available at: http://sciencing.com/science-electrolyte-levels-sports-drinks-7969703.html


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Available at: https://www.otsuka.co.jp/en/product/ionwater/


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